A message regarding the Cumulative Net Investment Loss (CNIL) calculation will present in the Warnings area of the review where investment related expenses exceed investment income. Is this the message you are referring to?
Once your return is filed and assessed by the CRA, the CNIL calculation will be updated on your account. If you want to maintain an accurate CNIL calculation within your Turbotax account, you can "Review" the message and input the details required.
The CNIL may affect your capital gains deduction. Here is a link to the CRA's information to learn more: Claiming a capital gains deduction - Canada.ca
